Abstract Asymmetriccelldivisions(ACDs)drivecellfatespecificationandtheformationofcomplextissuearchitectures. This often requires orienting the mitotic spindle to position daughter cells and/or segregate cell fate determinants. ACD?s drive the stratification and differentiation of the epidermis during embryogenesis. Additionally, oriented divisions have been observed to be associated with the production of hair follicle stem cell progenitors. However, whether spindle orientation is required for the production of these stem cells and how this is coupled to their cell fate remains unknown. During spindle positioning, astral microtubules of the mitoticspindleinteractwithspecificregionsofthecellcortex.However,wehaveanincompleteunderstanding of how microtubule dynamics and force production are controlled to precisely position mitotic spindles. My preliminarydatashowsthatKinesinFamilyMember18B(KIF18B),whichpromotesmicrotubulecatastrophes, is required for proper spindle orientation in cultured epidermal cells. Furthermore, KIF18B mutant mice have defects in the number and position of hair follicle stem cells, for the first time functionally linking spindle orientationtostemcellproduction.IhypothesizethatKIF18B-inducedmicrotubuledepolymerizationisrequired for spindle positioning, which in turn directs cell fate determination. Here I will examine both the molecular mechanism of KIF18B?s role in spindle orientation, and use KIF18B mutant mice to determine how spindle orientationislinkedtoproductionofhairfolliclestemcells.